The invention relates to dielectric waveguide antennas and more particularly to millimeter wavelength antennas that have a rotatable drum.
Dielectric waveguide antennas are described in U.S. Pat. Nos. 6,211,836 and 5,959,589 issued Apr. 3, 2001 and Sep. 28, 1999 respectively and assigned to the assignee of the present application. The above-noted patents are incorporated herein by reference.
Such antennas operate by coupling electromagnetic waves out of a dielectric waveguide to a rotating drum and radiating the coupled energy in patterns determined by features on the surface of the drum.
The efficiency of these antennas depends on the VSWR and scattering losses created when inputting electromagnetic signals into the waveguide.
Accordingly, a need exists for an improved drum-type dielectric waveguide antenna that has reduced input signal coupling losses and a lower VSWR compared to prior art antennas of the rotating drum type.
A rotatable drum dielectric rod waveguide antenna assembly with an improved input wave coupler is described.
The antenna assembly comprises an input wave coupler into which an electromagnetic wave is launched, a dielectric waveguide, and a rotating metallic drum, in close proximity to the waveguide, to control radiated electromagnetic energy between the waveguide and drum.
The input wave coupler of the invention further comprises a horn-shaped element and a metal extension for matching the characteristics of a feeding waveguide to those of the dielectric waveguide. The coupler operates to reduce VSWR return losses and scattered radiation from edges of the drum.
Additional embodiments of the invention include a reflector and a cylindrical lens to form and direct radiation out of the waveguide and drum.